Heretofore, pilot operated safety relief valves have been provided in pressure relief systems. Examples of prior art pilot operated relief valves are disclosed in U.S. Pat. No. 4,848,397 dated Jul. 18, 1989, and U.S. Pat. No. 5,842,501, dated Dec. 1, 1998. While these types of relief valves have proven effective in applications where the fluid product is a gas, they are not suitable for use in some liquid applications, e.g., oil supply lines.
Liquid product pipelines must be protected from liquid surge, typically caused by pump failure, rapid block valve closing, non-return check valve hard shutting, emergency shut down of a tank or loading system, or even a pump coming on or tripping. The magnitude of surge pressures vary—some are virtually undetectable, while others are severe enough to cause major damage. These propagating waves, either increasing or decreasing rapidly, are commonly known as hydraulic transient surges or water hammers that can cause severe damage to liquid product pipelines, vessels, flanges, valving, and associated equipment. Pilot operated safety relief valves don't operate quickly enough to open and relieve the pressure.
What is needed, then, is a surge relief valve in a pressure relief system for a pressure vessel, more particularly an improved surge relief valve for use in liquid product pipelines, and, even more particularly, a surge relief valve having a dome gas-filled reservoir arranged to bias the main valve closed until a set relief pressure is sensed, and then to open to relieve the overpressure, and finally to force the main valve to close when the overpressure has dissipated.